Arc controlling electrodes for switches and gaps



Dec. 17, 1968 s. R. SMITH. JR

ARC CONTROLLING ELECTRODES FOR SWITCHES AND GAPS Original Filed April 16, 1965 fall/442,4..

i United States Patent Office 3,417,216 Patented Dec. 17, 1968 ABSTRACT OF THE DISCLSURE The electrodes are cup shaped with spirally slotted inturned or reentrant lip portions in mouth to mouth relation for electromagnetically driving an arc between them toward their common axis and rotating it about that axis.

This invention relates to electric arcs and more particularly to their auto-confinement and control.

This is a division of application Ser. No. 448,787 filed April 16, 1965, now Patent No. 3,366,762, granted Jan. 30, 1968, and assigned to the same assignee.

An example of where arc control is important is in vacuum switches, but the invention is not limited to such switches and can be used in ordinary switches or in gap devices such as are found in lightning arresters or in other electrical devices where confinement and control of an electric arc is desirable. A reason why arc control is particularly important in vacuum switches is that because of the comparatively high vacuum that must be maintained their volume, and hence size, should be as small as possible. On the other hand, high energy arcs tend to spread and get out of -control and vaporize the electrodes carrying metal vapor onto the insulating walls of the housing, inviting failure to interrupt. These factors, therefore, limit the interrupting capacity of a given size vacuum switch of ordinary construction. By preventing the arc from spreading, the size of a vacuum switch of given interrupting ability can be substantially reduced.

An object of the invention is to provide Aa new and improved means for confining and controlli'g a electric arc.

Another object of the invention is to provide a novel electromagnetic means for self-controlling and confining an electric arc.

A further object of the invention is to provide a novel arcing electrode configuration.

An additional object of the invention is to provide an improved electric switch contact configuration.

An added object of the invention is to provide a new and improved vacuum switch of increased interrupting ability per unit size.

In accomplishing the objects of the invention at least one cup shaped electrode with a re-entrant lip portion cooperates with another electrode for automatically confining by inherent electromagnetic action an arc between the electrodes to the space between the electrodes. By making one of the electrodes a rod shaped contact and confining the arc to the interior of the cup shaped electrode as the other contact, the latter will also function as a metal vapor shield in a vacuum switch thus making it possible to eliminate such a shield as a separate element in vacuum switches.

The invention will be better understood from the following descroiption taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing,

FIG. 1 is Ia perspective View of a vacuum switch employing the invention,

FIG. 2 is a longitudinal sectional view of the switch shown in FIG. 1 taken on line 2 2 of FIG. 1, and

FIGS. 3 and 4 are respectively Orthographie and isometric half sectional views of another modification employing a pair of cup shaped electrodes or contacts.

Referring now to the drawings, and more particularly t0 FIG. l, there is shown therein a vacuum switch 1 comprising by way of example a cylindrical housing 2 of suitable insulating material such as glass or ceramic material provided with metallic end caps 3 which lare sealed to the ends of the housing 2 in any suitable manner so as to form a vacuum tight envelope or enclosure. Extending from the lower end of the enclosure is an electri- .caal terminal connection 4 and extending from the upper end of the enclosure is an electrical terminal connection 5. The terminal 4 is fixed and the terminal 5 is movable by means of a bellows 6, the lower end of which is sealed to the upper end cap or plate 3 and the upper end of which is sealed to a flange 7 on the terminal connector 5.

The interior construction of the switch is shown in FIG. 2 and will be seen to consist of a cup shaped metallic or conducting electrode or contact 8 from the center of whose bottom extends outwardly the terminal connection 4. The portion of the terminal connection 5 which extends into the switch is aa rod like conductive member 9 which extends into the cup electrode 8 and on the lower end of which adjacent the bottom of the cup shaped electrode 8 is an arcing electrode or contact portion 10 shown as being dumbbell shaped in cross section but, of course, being actually circular with indented central portions on both sides. Attached to the rim of the cup 8 is a metallic or conductive re-entrant inwardly extending lip portion 11 surrounding the rod 9 and extending inwardly toward the bottom of the cup member 8. The switch can be closed by moving the parts 5, 9 and 10 downwardly until part 10 contacts the bottom of the cup 8 or moving the parts 5, 9 and 10 upward until the upper edge of the part 10 engages the lower end of the inwardly extending reentrant lip portion 11. FIG. 2 shows the switch in its open position where there is no contact between the parts V1t) and the parts 8 or 11.

The operation of FIG. 2 as thus far described is as follows. Assume that the switch attained its illustrated open position by raising the arcing contact member 10 from the bottom of the cup `8. This will initially draw an arc 12 which will be fed by current having a curved or kinked path in that the lcurrent will flow generally horizontally through portions of the member 10 and the bottom of the cup 8 between the rod `9 and the arc 12 and between the arc 12 and the terminal connection 4. As a result of this so-called current loop, the magnetic flux density on the inner side of the loop corresponding to the right-'hand side of the Iarc 12 as viewed in FIG. 2 will be greater than the flux density on the opposite side so that an 4automatically produced electromagnetic force will tend to move the arc to the left as viewed in FIG. 2, i.e., clockwise -about the end of the electrode or contact 10 so that the arc will successively assume positions 13, 14, 15 and 16. However, in the position 16 the arc will be fed through the re-entrant lip portion 11 which extends in the opposite direction from the wall of the cup shaped member 8 so that the electromagnetic force will `reverse and the arc will be forced back to the position 15. Then the original force which caused it to jump from position 15 to position 16 will again come into play so that the arc will rapidly jump back and forth between positions 15 and 16.

Even if the arc were to over-shoot the position 16 to a position 17 between the lip portion 11 and the rod 9, the electromagnetic force would be such as to drive the `are downward and back to position 15.

Essentially the same action would take place if the switch had come from an upward closed position where movable contact was touching the lower end of the reentrant lip portion 11 to the open position shown in FIG. 2, except that in that case the arc would first be drawn at position 16 and would then be forced to jump to position and back and forth between those positions 3S already described.

The result is that the arc is confined within the cup shaped electrode or contact 8 so that little or no contact metal vaporized by heat of the arc can escape from the cup but all such vaporized metal will simply condense on the metallic surfaces within the cup. Consequently the conventional metal shield which is normally interposed between the contacts of a vacuum switch and its insulating envelope such `as the insulating cylinder 2 can be eliminated. The function of such a shield is, of course, to condense vaporized metal and prevent it from condensing on and coating the surfaces of the insulating cylinder or envelope so as to cause ultimate short circuiting or failure of the switch. It also tends to avoid weakening of the ceramic by heat shock.

If desired, means may be provided for rotating the arc about the common axis of the cup 8 and rod 9. One such means can be a conductive coil 18 for immersing the arc in a magnetic field which extends generally paraln lel to the common axis of the cup 8 and rod 9, this coil being connected serially in the circuit. The interaction of the horizontal component of the a-rc current and the Vertical magnetic field will cause a tangential force to be applied to the arc, thus rotating it or spinning it about the axis of the switch. This, ofcourse, has the desirable effect of keeping the electrodes from melting or burning away at a particular point because it does not continuously play between fixed spots on the electrodes.

Ordinarily in the case of alternating current, the arc will be extinguished at the first current zero.

If desired, the rod 9 can be provided with a shield 19 for condensing what small amount of vaporized metal may escape from between the rod 9 and the lip 11.

Preferably the radial distance between the rod 9 and the lip portion 11 is smaller than the radial distance between the lip portion 11 and the wall of the cup member 8, and preferably the axial length of the lip portion 11 is a sizable fraction of the arc chamber height.

In the modification shown in FIG. 3, there are two cup shaped electrodes and 26 with re-entrant inwardly extending lip portions 27 and 28 respectively. They are arranged in mouth facing mouth relation and when spaced as illustrated constitute a gap so that current owing between a terminal 29 for electrode 25 and a terminal 30 for an electrode 26 will jump the gap between them. However, they obviously may be the contacts of a switch in which case they will be -relatively movable in their coaxial direction so that when they are in contact the switch will be closed 'and when they are separated the switch will be open. They can, of course, be located in an evacuated envelope as in the preceding figures so as to constitute a vacuum switch. It will be understood, of course, that FIG. 3 is an Orthographie sectional view through the central axis and that actually the cups have re-entrant surfaces extending all around a common axis as shown by the isometric sectional view in FIG. 4. Consequently when they are separated as shown in FIG. 3 they constitute a special type of horn gap having a lateral dimension which is actually a closed re-entrant surface, this being a surface of revolution if the cups are circular in horizontal cross section. The re-entrant portions 27 and 28 are preferably provided with complementary sloping angular or spiral cuts or slots 31 and 32 respectively for the purpose of spinning an arc around the common longitudinal axis which, of course, is a central vertical axis as viewed in the drawing. The direction of rotation is as indicated by the arrowed circle at the bottom of FIG. 4.

The operaton of FIG. 3 is as follows. Assume -an arc 33 is drawn or struck between the electrodes 25 and 26. rl`his is at a point of minimum spacing and it will be seen that current flowing into and out of that arc between the terminals 29 and 30 along the sides of the cups 25 .and 26 will have a loop or kink thus forcing the varc inward toward the center or common axis so that the arc will rapidly progressively assum'e the dashed line positions 34, 35, 36 and 37. This same action would take place regardless of where on the perimeters of the mouths of the -cups 25 and `26 the arc 33 initially forms. At the same time the arc is caused to move along this perimeter or, in other words, rotate :about the common axis because the skewed teeth or cuts 31 and 32 produce tangential components in the direction of current flowing into and out of the arc. These tangential components have the same direction because the angles of skewing of the cuts or teeth are such as to take account of the directions of the current when it enters and when it leaves the arc.

Of course, the higher the arc current, the greater the electromagnetic force tending to force the arc inward toward the center and also the greater the force tending to spin it about the axis. In this manner, the arc is automatically and practically instantaneously driven inward, elongated, and cooler by the horn gap action supplemented by the spinning action so that the arc can go completely around the electrode axis many times in a half cycle of cycle current.

To facilitate manufacture it is preferable to make the upper and lower halves of FIG. 3 exact duplicates (except for cuts 31 and 32 which are in opposing relation) as shown but this, of course, is not necessary.

The vacuum switches can, of course, be evacuated in any suitable manner such as by pumps of either the mechanical or the diffusion type or both in series or in a pumpless manner according to the method disclosed and claimed in De Santis et al. U.S. Patent 2,934,392 which is assigned to the present assignee.

It will, of course, be understood that the previously used terms horizontal and vertical refer only to the drawings when they are placed in an upright position and that actually the invention in nowise depends on any particular orientation of the devices in space.

While there have been shown and described particular embodiments of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention, and therefore it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a pair of spaced-apart coaxially aligned cup shaped arcing duty electrodes in mouth facing mouth relation, each electrode mouth having a re-entrant lip portion extending from the rim thereof inwardly and toward the bottom and central axis of the electrode, each electrode having a wall portion with a diameter substantially larger than the diameter of its mouth, the shortest arc-over path between said electrodes being between the respective electrode mouths whereby an arc initiated between said electrodes first occurs between said electrode mouths or inwardly therefrom, and the current path through such an arc follows an inwardly curved path which causes a magnetic eld to be developed that immediately drives the feet of the arc onto said lip portions.

2. In combination, a pair of spaced-apart substantially identically shaped coaxially aligned circular cross section cup shaped arcing duty electrodes in mouth facing mouth relation, each electrode mouth having a re-entrant lip portion extending from the rim thereof inwardly and toward the bottom and central axis of the electrode, each electrode having a wall portion with a diameter substantially larger than the diameter of its mouth, the shortest arc-over path between said electrodes being between the respective electrode mouths whereby an arc initiated between said electrodes first occurs between said electrode mouths or inwardly therefrom, and the current path through such an arc follows an inwardly curved path which causes a magnetic field to be developed that immediately drives the feet of the arc onto said lip portions.

3. The combination as in claim 1 provided with means for causing an arc between said electrodes to rotate about their common axis, said means comprising a plurality of skewed teetth (31 and 32) formed in each of said lip portions and adapted to produce tangential components in the direction of current ow respectively toward and away from said arc.

4. In combination, a pair of coaxially aligned and coaxally relatively movable cup shaped arcing duty make yand break switch contacts in mouth to mouth relation, each contact cup mouth having a re-entrant lip portion extending inwardly toward the bottom and central axis thereof whereby when said contacts are separated the space between their mouths constitutes a horn gap having a re-entrant lateral surface, each of said contacts having a wall` portion with a diameter substantially larger than the diameter of the contact mouth, the shortest arc-over path between said contacts being between the respective contact mouths whereby an arc initiated between said contacts first occurs between the contact mouths or inwardly therefrom, and the current path through such an arc follows an inwardly curved path which causes a magnetic field to be developed that immediately drives the feet of the arc onto said lip portions.

5. In combination, a pair of coaxially aligned and coaxially relatively movable circular cross section cup shaped arcing duty make and break switch contacts in mouth to mouth relation, each contact cup mouth having a re-entrant lip portion extending inwardly toward the bottom and central axis thereof whereby when said contacts are separated the space between their mouths constitutes a horn gap having a re-entrant lateral surface of revolution, each of said contacts having a wall portion with a diameter substantially larger than the diameter of its respective contact mouth, the shortest arc-over path between said contacts being between the respective contact mouths whereby an arc initiated between said contacts first occurs between the contact mouths or inwardly therefrom, and the current path through such an arc follows an inwardly curved path which causes a magnetic field to be developed that immediately drives the feet of the arc onto said lip portions.

6. The combination as in claim 4 provides with means for causing an arc between said contacts to rotate about the common axis thereof, said means comprising a plurality of skewed teeth (31 and 32) formed in each of said lip portions and adapted to produce tangential components in the direction of current flow respectively toward and away from said arc.

References Cited UNITED STATES PATENTS 3,185,798 5/1965 Titus.

ROBERT S. MACON, Primary Examiner.

U.S. Cl. XR. 200-166 

